Optical Beamforming Concepts for Wide-Swath Synthetic Aperture Radar Systems

Abstract

High-resolution wide-swath (HRWS) imaging using scan-on-receive (SCORE) synthetic aperture radar (SAR) with one or multiple simultaneous beams is being heavily investigated using digital beamforming paradigms. However, a contender is analogue beamforming using photonics. In this work, the feasibility of photonics enhanced beamforming in SAR systems in higher frequency bands and bandwidths is investigated using a state-of-the-art SAR system as a comparison. The most common performance indicators are derived and an example SAR system is devised, with a discussion on potential antenna configurations. The integrated microwave photonics (IMWP) platforms available and most suited to SAR systems is discussed, including architectures and materials. Additionally, an investigation into system noise and dynamic range performance reveals a number of essential challenges that need to be addressed, including the reduction of losses an thereby the required number of semiconductor optical amplifiers (SOA) and the noise performance of the laser(s). The reconfiguration speed of beamforming phase shifters and true-time delay (TTD) elements are essential for SCORE operation with a large number of beams, which limits the viable materials used for these elements. The current state of IMWP indicate that these advanced systems with many beams and channels is very difficult to realize for SAR and implementations in simpler systems are more viable. However, the rapid development of IMWP indicate that these beamforming systems will soon be viable for SAR.